Purpose:The tardigrade Richtersius coronifer has previously been shown to tolerate very high doses of low linear energy transfer (low-LET) radiation (gamma rays). The purpose of this study was to extend our knowledge on radiation tolerance in this species by investigating the dose-response to high-LET radiation in terms of protons.

Materials and methods:Dehydrated tardigrades of the species R. coronifer were irradiated with 2.55 MeV (megaelectronvolts) protons at doses ranging from 500 gray (Gy) to 15,000 Gy, to investigate the dose-viability relationship. In addition, a focused proton microbeam was utilised to determine the areal mass distribution, using the ion beam analytical technique STIM (Scanning Transmission Ion Microscopy).

Results:The experiment suggests that R. coronifer is unaffected by doses of proton irradiation up to 10,000 Gy, but shows very little viability at higher doses. The STIM analysis revealed that the thickness of the dehydrated tardigrades exceeds 150 μm, and that a fraction of the protons may not be fully absorbed.

Conclusion:Our results are in line with previous studies of exposure to high-LET radiation in tardigrades, indicating that these animals are equally or even more tolerant to high-LET compared to low-LET gamma radiation. The physiological background to this remarkable result is currently unknown, but deserves investigation.